The resistance of sensors based on Magnetoresistance (MR), such as Giant Magnetoresistance (GMR) or Tunnel Magnetoresistance (TMR) sensors, varies when an external magnetic field is applied to the sensor device. GMR/TMR “spin valve” sensors typically have two magnetic layers separated by a non-magnetic layer. The two magnetic layers are made from materials having different hysteresis curves so one layer (“soft” layer) changes polarity while the other (“hard” layer) has a fixed polarity.
As large a measuring range as possible is desirable, along with high accuracy. In practice, however, the accuracy of known GMR/TMR devices can be limited by hysteresis, and the measuring range can be limited by the saturation field strength.